To evaluate this, plug in the number 4 for the variable a and the number 5 for the variable 5.
6a + 3ab
6(4) + 3(4)(5)
To solve this multiply then add.
Multiply from left to right and don't add until everything has been multiplied.
Basically, 6(4) + 3(4)(5) = (6 • 4) + (3 • 4 • 5).
6 • 4 = 24
3 • 4 = 12
12 • 5 = 60
Now we have 24 + 60.
Just add and you have your answer!
24 + 60 = 84
So when a is 4 and b is 5, 6a + 3ab is equal to 84.
Hope this helps!